The hedgehog signaling pathway is essential for numerous processes during embryonic development. Members of the hedgehog family of secreted proteins control cell proliferation, differentiation and tissue patterning. The pathway was first deciphered in the fruit fly Drosophila, but since has been shown to be highly conserved in invertebrates and vertebrates, including humans. The overall activity of the hedgehog signaling pathway declines after embryogenesis in most cells, but the pathway remains active in certain adult cell types. Recently, it has been shown that uncontrolled activation of the hedgehog pathway results in certain types of cancer as detailed below.
The Hedgehog polypeptide is a secreted protein that functions as a signaling ligand in the hedgehog pathway. Exemplary hedgehog genes and proteins are described in PCT publications WO 95/18856 and WO 96/17924. Three different forms of the hedgehog protein are found in humans; Sonic hedgehog (Shh), Desert hedgehog (Dhh) and Indian hedgehog (Ihh). Sonic hedgehog is the most prevalent hedgehog member in mammals and also is the best characterized ligand of the hedgehog family. Prior to secretion, Shh undergoes an intramolecular cleavage and lipid modification reaction. The lipid modified peptide is responsible for all signaling activities
Two transmembrane proteins are involved in signal transduction of in the hedgehog pathway; the twelve-transmembrane Patched receptor (Ptc) and the seven-transmembrane Smoothened protein (Smo).
The findings in the art suggest that Hedgehog acts by binding to Ptc, thereby releasing an inhibitory effect of Ptc on Smo. Since Ptc and Smo are both transmembrane proteins, a proposed scenario is that they physically associate to form a receptor complex, though indirect mechanisms of action are also plausible. The derepression of Smo from Ptc inhibition most likely involves a conformational change in Smo. Ptc, however, is not essential for Smo's activity, since Smo becomes constitutively activated in the complete absence of Patched protein (Alcedo et al., supra; Quirk et al. (1997) Cold Spring Harbor Symp. Quant. Biol. 62: 217–226). Once Smo is derepressed it is rapidly and highly phosphorylated and transduces a signal that activates transcription via the Gli transcription factors (homologue of Dropophila Ci protein) (Alexandre et al. (1996) Genes Dev. 10: 2003–13)). The Gli1 transcription factor up-regulates many genes involved in growth and development (Alexandre et al., supra). Hedgehog signaling is essential in many stages of development, especially in formation of left-right symmetry. Loss or reduction of hedgehog signaling leads to multiple developmental deficits and malformations, one of the most striking of which is cyclopia (Belloni et al. (1996) Nature Genetics 14: 353–6).
Recently, it has been reported that activating hedgehog pathway mutations occur in sporadic basal cell carcinoma (Xie et al. (1998) Nature 391: 90–2) and primitive neuroectodermal tumors of the central nervous system (Reifenberger et al. (1998) Cancer Res 58: 1798–803). Uncontrolled activation of the hedgehog pathway has also been shown in numerous cancer types such as GI tract cancers including pancreatic, esophageal, gastric cancer (Berman et al. (2003) Nature 425: 846–51, Thayer et al. (2003) Nature 425: 851–56) lung cancer (Watkins et al. (2003) Nature 422: 313–317, prostate cancer (Karhadkar et al (2004) Nature 431: 707–12, Sheng et al. (2004) Molecular Cancer 3: 29–42, Fan et al. (2004) Endocrinology 145: 3961–70), breast cancer (Kubo et al. (2004) Cancer Research 64: 6071–74, Lewis et al. (2004) Journal of Mammary Gland Biology and Neoplasia 2: 165–181) and hepatocellular cancer (Sicklick et al. (2005) ASCO conference, Mohini et al. (2005) AACR conference).
Small molecule inhibition of hedgehog pathway activity has been shown to result in cell death in a number of different cancer types having uncontrolled hedgehog pathway activation (See, for example, Berman et al., 2003 Nature 425: 846–51).
Hedgehog pathway antagonists are currently being explored in a large number of clinical conditions where a therapeutic effect can be obtained for a condition or disorder by inhibiting one or more aspects of Hedgehog pathway activity. Although the primary focus has been on cancer, investigators have found that small molecule inhibition of the hedgehog pathway has been shown to ameliorate the symptoms of psoriasis (Tas, et al., 2004 Dermatology 209: 126–131, published US patent application 20040072913 (herein incorporated by reference)). Psoriasis is a very common, chronic skin disorder typically characterized by skin lesions usually containing erythematous papules and plaques with a silver scale, although there are variations both on the skin and in other parts of the body. Psoriasis is currently thought to be an autoimmune disease but its etiology is still poorly understood.
A hedgehog pathway inhibitor that has attracted considerable interest is the natural product cyclopamine. Cyclopamine was first isolated from the lily Veratrum californicum in 1966 after it was found that the offspring of grazing sheep were born with severe birth deformities. In an effort to identify the agent(s) responsible for causing these birth deformities, the FDA investigated possible sources of tetragens and identified the jervine family of steroidal alkaloids, including the compound cyclopamine, as the tetragens responsible for the birth deformities.
Much later, it was found that cyclopamine's mechanism of action was through the inhibition of hedgehog pathway activity (Cooper et al. (1998) Science 280: 1603–7, Chen et al., (2002) Genes and Development 16: 2743–8). Cyclopamine and related compounds have been shown to have anticancer activities through action on the hedgehog pathway. Despite initial promise, no members of this family of compounds, or analogues thereof, have been successfully developed as an anticancer agent. The present invention fulfills this need and has other related advantages.